| 1771 | Joseph Priestley | Plants "restore" air (release O2); discovered O2 by placing plants with candles/mice | Background concept |
| 1779 | Jan Ingenhousz | Photosynthesis requires light; discovered that leaves release O2 only in light | Light dependency of photosynthesis |
| 1804 | Nicolas de Saussure | CO2 and H2O are raw materials; quantified the inputs | Reactants identified |
| 1837 | Dutrochet | Photosynthesis occurs only in cells containing chlorophyll (green cells) | Role of chlorophyll established |
| 1845 | Robert von Mayer | Photosynthesis converts light energy to chemical energy | Energy conversion concept |
| 1882 | T.W. Engelmann | Bacteria experiment with prism + Spirogyra → action spectrum first determined | Action spectrum concept |
| 1931 | Cornelis van Niel | O2 comes from H2O (not CO2); generalised photosynthesis equation | Direct NEET topic |
| 1937 | Robert Hill | Isolated chloroplasts can reduce artificial acceptors (Hill reaction — photolysis of water) | Hill reaction definition |
| 1941 | Ruben and Kamen | ^{18}O labelling confirms O2 from H2O (not CO2) | Confirms Van Niel |
| 1954 | Daniel Arnon | Non-cyclic and cyclic photophosphorylation demonstrated in isolated chloroplasts | ATP synthesis in chloroplasts |
| 1957 | Emerson | Enhancement effect → proposed two photosystems | Basis of Z-scheme |
| 1954–1961 | Melvin Calvin | Calvin cycle mapped using ^{14}CO2 chromatography; Nobel Prize 1961 | Direct NEET topic |
| 1960s | Hatch and Slack | C4 pathway described (OAA as first stable product in maize) | C4 pathway named after them |
| 1966 | Mitchell | Chemiosmotic hypothesis for ATP synthesis | Proton gradient / ATP synthesis |